The story of Stephen Hawking, the great theoretical physicist who died Wednesday morning at age 76, has an Israeli angle going back decades. The subject of his best-known and most important research, showing that black holes emit radiation — known as Hawking radiation or Hawking–Bekenstein radiation — is based on research by the Hebrew University physics professor Jacob Bekenstein, who died in 2015.
Hawking published his theory in 1974: Black holes emit particles, he postulated (which had not been thought possible because of their terrific gravitational pull) and would eventually be doomed to vanish unless they gain mass, for instance from celestial bodies getting sucked in.
At first Hawking actually scorned Bekenstein’s ideas regarding the thermodynamics of black holes. But when the English theoretical physicist set out to disprove them, he was instead won over, says Tel Aviv University physics professor Marek Karliner.
It bears adding that everything from the existence of black holes to radiation from them is still theoretical, and has not been proven.
“Hawking’s work is profoundly tied with that of Bekenstein, who studied the temperature of black holes. ... Without Bekenstein’s work, Hawking’s work on black holes probably would never have come about,” Karliner says.
Despite using a wheelchair for mobility and being almost completely paralyzed by Lou Gehrig’s disease, Hawking visited Israel several times. “I knew him well,” says Prof. Tsvi Piran of Hebrew University’s Racah Institute of Physics. He met Hawking in the 1970s and was the first to invite him to Israel, in the early ‘80s. “He first visited Israel in 1983. He was a lot less well-known then,” Piran says.
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By the time of his second visit, in the late 1980s, Hawking had already published his famous book “A Brief History of Time: From the Big Bang to Black Holes” and was quite famous. On his third visit to Israel, in 2007, Hawking was Piran’s guest. “I remember we took him to Masada and lifted him, on his wheelchair, from the cable car. We visited the Old City of Jerusalem,” says Piran, who also visited Hawking in Cambridge several times.
Hawking also visited Israel in 2012, to receive the Wolf Prize in Physics, awarded by the Wolf Foundation in Israel, a private nonprofit organization founded by Ricardo Wolf, a Jewish-Cuban inventor.
Hawking’s theory that black holes emit radiation is the only connection made so far between quantum theory and general relativity, says Piran. However, the very connection involves a paradox, he says: The principles of quantum theory cannot all coexist with the principles of relativity, which has led to decades of squabbling in the physics crowd.
At first Hawking argued that the principles of relativity dominate, Piran says. Over time, he admitted his mistake and accepted the dominance of quantum theory. Even so, a problem remains that has bedeviled theoretical physicists for 45 years: What happens to information when it falls into a black hole that eventually evaporates?
Karliner begs to draw a distinction between Hawking’s immense public popularity and his concrete contributions to science.
Hawking may well have been more famous even than Albert Einstein, Karliner says. But: “In the scientific community, everybody has the greatest respect for the fact that he overcame the disease,” he says (working on for decades despite being ill). “It is true that his work on Hawking radiation took the scientific community by shock. But the truth is that, most probably, without Bekenstein’s work, Hawking’s work would not have happened.”
The scientific establishment hasn’t managed to prove Hawking’s ideas yet, despite many attempts to simulate tiny black holes, including in Israel. It all remains theoretical — which is presumably why Hawking was never awarded the Nobel Prize.
Theoretical physicists have won the Nobel only when experiments have confirmed their theories, explains Karliner. “In Hawking’s case, confirmation by experiment is extremely difficult because [the radiation emission by black holes] that he hypothesizes is very weak and slow. ... If the radiation that Hawking postulated had been proved, there’s no question that he would have been awarded the Nobel, because his prediction is nothing short of astonishing. But in physics, the experiment is what counts. Those are the rules of the game.”
Hawking outlived his prognosis by decades. He was diagnosed with Lou Gehrig’s disease, an incurable degenerative condition also knows as amyotrophic lateral sclerosis, at 21, and was expected to die within a few years.